Tokyo Firm Puts Detectors to Work in Healing Sick Building Syndrome

Energy conservation efforts in the home or office often entail sealing up buildings, which can trap pollutants such as formaldehyde and lead to a condition known as sick building syndrome. Identifying the pollutant can be a challenge for small companies that are doing remediation and renovation, according to Naohide Shinohara of Japan’s National Institute of Advanced Industrial Science and Technology in Tsukuba.

Researchers have developed a visual formaldehyde detector that changes color based upon the concentration of formaldehyde. The sensor can be read visually or the results assessed quantitatively using a reflectance photometer. Images courtesy of Naohide Shinohara, National Institute of Advanced Industrial Science and Technology.Now Shinohara and his colleagues at Tokyo-based Nippon Living Co. Ltd. and at the University of Tokyo have developed a possible way to identify indoor pollutants. They recently demonstrated a passive sensor and a reflectance photometer that measure the emission rate of formaldehyde.

“There are some methods to measure the emission rates,” Shinohara said. “These methods, however, need laboratory analysis. Thus, they cannot be used by the general public.”

Because formaldehyde can come from various products, there are many potential emission sources. Dangerous levels can occur in old and new structures, such as the mobile homes deployed along the Gulf Coast as temporary housing after Hurricane Katrina. In Japan and elsewhere, the limit for long-term exposure is 0.08 parts per million (ppm). At about 0.1 ppm, the chemical can irritate eyes, cause headaches and lead to difficulty breathing.

In devising their scheme, the researchers elected to use a color changing device to indicate emission rate. Consequently, a quick visual check might be enough. For a more precise determination, they developed an inexpensive colorimetric sensor.

The group, Shinohara noted, had experience with passive devices that measure indoor pollutant concentration. Nonetheless, the development of the formaldehyde sensor was difficult because of three requirements. The investigators needed to develop a small monitor with adequate sensitivity as well as a stable and sensitive colorimetric sensor. The monitor also ideally had to be specific only to formaldehyde.

Because of the sensitivity and specificity requirements, they used an enzyme reaction. They settled on one that produced formazan in the presence of formaldehyde, thus rendering a colorless material red when formaldehyde was present. This decision, in turn, meant that they had to use a glass fiber sheet as a way to retain the water needed for the reaction.

Detecting formaldehyde

They constructed a sampler with a body made out of the plastic polyethylene terephthalate. Measuring 23 mm, the body had a 5-mm hole, exposing the test sheet to the air and to any formaldehyde in the air. In operation, they placed a drop of water in the sampler, set the monitor down in an area and removed it after 30 min. If formaldehyde was present, the test material would have changed color, with a redder hue indicating a higher emission rate. The group describes its work in the May 8, 2008, ASAP edition of Environmental Science & Technology.

The investigators also developed a portable reflectance photometer. For this, they used a green LED operating at 540 nm and two detectors: one a photodiode that measured reflectance, the other, a detector that determined the intensity of the light source.

When they tested their method, they found that it gave results comparable to those resulting from laboratory techniques. The limit of detection was about one-tenth the allowed amount, indicating that the new method was suitable for screening materials and objects.

Shinohara noted that the formaldehyde detection technique is commercially available from Nippon Living. As for the researchers, they are working on developing sensors for other chemicals, such as organic phosphorus, and for other causes of indoor air problems.

“We are trying to develop a sensor for allergens, such as mold,” Shinohara said.